Access to view requests across all sites

I would like to use the Sites feature for our environment, rather than have one site for everyone. However, one flaw is that users (i.e. Requesters) cannot be configured to show all requests, across all sites (only their own, their department, and their site).

Our current Helpdesk application allows all of our users to view all requests. This helps reduce the number of duplicate tickets for the same issue, if previously reported; granted, not all of our users sift through existing tickets. However, having the option to view all requests for all sites would be very useful.

I haven't tried to reproduce this in our environment yet, but what happens if a user in Site B receives a CC request email for an incident associated to Site A? Will that user be able to view the ticket details and send replies? This would especially be a problem for a manager or supervisor that has team members located in different sites.